<template>
  <div class="list">
    <ul>
      <li
        class="item"
        v-for="item of letter"
        :key="item"
        :ref="item"
        @touchmove="handleTouchMove"
        @touchstart.prevent="handleTouchStart"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
      >
        {{ item }}
      </li>
    </ul>
  </div>
</template>

<script>
export default {
  name: "CityAlphabet",
  props: {
    cities: Object
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    };
  },
  computed: {
    letter() {
      const letters = [];
      for (let i in this.cities) {
        letters.push(i);
      }
      return letters;
    }
  },
  methods: {
    handleLetterClick(e) {
      this.$emit("change", e.target.innerText);
    },
    handleTouchStart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        const startY = this.$refs["A"][0].offsetTop;
        const touchY = e.touches[0].clientY - 79;
        const index = (touchY - startY) / 20;
        if (index >= 0 && index < this.letters.length) {
          this.$emit("change", this.letters[index]);
        }
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>

<style lang="stylus" scoped>
@import '~@/assets/variable.styl'
.list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
        line-height: .4rem
        text-align center
        color: $bgColor
</style>
